1. Field of the Invention
The present invention relates to a ceramic composition that is used at high frequency regions, such as a microwave region and a millimeter wave region, and to a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication system that are composed of the ceramic composition.
2. Description of the Related Art
Dielectric ceramics are widely used as components of, for example, dielectric resonators and circuit boards at high frequency regions, such as a microwave region and a millimeter wave region.
When such a high-frequency dielectric ceramic is applied particularly to a dielectric resonator or a dielectric filter, the following characteristics are required:
1) Since wavelengths of electromagnetic waves are reduced by 1/(∈r)1/2 in a dielectric with a relative dielectric constant ∈r, the relative dielectric constant should be large enough to meet the demand for miniaturization;
2) Dielectric loss should be small, that is, the Q-factor should be high; and
3) Temperature stability of the resonant frequency should be excellent, that is, the temperature coefficient of the resonant frequency (τr) should be about 0 ppm/° C.
Known dielectric ceramic compositions of this type include (Zr, Sn)TiO4 (Japanese Examined Patent Application Publication No. 4-59267), Ba2Ti9O20 (Japanese Unexamined Patent Application Publication No. 61-10806), Ba(Sn, Zr, Mg, Ta)O3 (Japanese Examined Patent Application Publication No. 6-74162), Ba(Zn, Mg, Ni, Zr, Ta)O3 (Japanese Examined Patent Application Publication No. 7-21970), and Ba(Zr, Mg, Ta)O3 (Japanese Patent No. 2965417).
While ceramic compositions of (Zr, Sn)TiO4 or Ba2Ti9O20 have large relative dielectric constants (∈r) of 36 to 40, they have low Q×f values of 50,000 to 70,000 GHz. Thus, their Q-factors are insufficient for use at high frequencies over 10 GHz. On the other hand, ceramic compositions of Ba(Sn, Zr, Mg, Ta)O3, Ba(Zn, Mg, Ni, Zr, Ta)O3 and Ba(Zr, Mg, Ta)O3 have large relative dielectric constants (∈r) of 20 to 30 and high Q×f values of 100,000 to 250,000 GHz. However, these compositions are based on expensive Ta and are therefore not suitable for commercialization.
In recent years, demands for electronics of low dielectric losses and small sizes have grown. There are also growing demands for dielectric materials with excellent dielectric properties, particularly for inexpensive dielectric materials that have both large relative dielectric constants (∈r) and high Q-factors. However, these demands are not fully satisfied yet.